The present invention relates to a temperature adjusting method and an apparatus therefor.
The manufacturing process of semiconductor devices includes heat treatments such as a chemical vapor deposit (CVD) and an oxidation treatment. One of the known examples of the device for carrying out the heat treatment in a batch scheme is a vertical type heat treatment equipment.
In the oxidation treatment using the above-mentioned device, a great number of wafers are, first, mounted on a wafer board in a rack-like manner, and the wafer board is loaded into a reaction tube having a double-tube structure. Subsequently, the inside of the reaction tube is heated to a predetermined temperature, for example, 800.degree. by a heater, and while exhausting through an exhaust tube, a treatment gas is introduced from a gas inlet tube, thus carrying out a process.
In the above-described process, the heat treatment is carried out while maintaining the inside of the reaction 1 stably at 800.degree.. During this process, it is necessary to control the temperature at a high accuracy, and therefore the heating is carried out while controlling the electric power supply amount to the heater by a control unit. In the control of the heater, it is ideal that a temperature sensor should be provided as close as possible to an object to be processed, that is, wafers. It is however very difficult to have such a structure, in which the temperature sensor is provided close to the wafers during a heat treatment, in terms of designing as well as the creation of contamination.
As a solution to the above drawbacks, the following countermeasures are conventionally taken. That is, a first thermo-sensor A made of, for example, a thermocouple is provided at a position close to wafers within the reaction tube, for example, on the wafer board, and a second thermo-sensor B is provided close to the outer surface of the reaction tube. Then, during the adjustment period before carrying out a process, the temperature of the thermo-sensor B, which is stabilized when the set temperature of the thermo-sensor A is stabilized, is obtained, and the difference between these temperatures is acquired in advance. Subsequently, the heater is controlled on the basis of the detection value of the thermo-sensor B during the process.
As described above, during the adjustment period, it is required that the temperature of the heater should be controlled so that the set temperature of the temperature sensor A is stabilized. During the temperature control, if only the detection signal of the thermo-sensor A is fed back so as to obtain the temperature difference, the detection value of the temperature sensor B is not easily stabilized. Therefore, when obtaining the temperature difference, the detection signals of both the thermo-sensors A and B must be fed back, and to achieve this, a cascade control system is employed.
In this case, first, a control parameter of a PID adjustment unit (PID value) is determined by use of the feedback loop of only the detection signal of the thermo-sensor A. The determination of the parameter is made by the operator by adjusting the PID value in a trial-and-error manner so that the temperature-increasing curve is optimized, as monitoring the change in the detection signal of the thermo-sensor A along with time. Then, in a similar manner, a PID value of the PID adjustment unit is determined with use of the feedback loop of the detection signal of the thermo-sensor B.
As described above, the temperature of the thermo-sensor B, which is stabilized when the set temperature of the thermo-sensor A is stabilized, is obtained. Therefore, at the time of a process, the thermo-sensor A is removed, and the reaction tube is heated while controlling the heater using the thermo-sensor B. Thus, the temperature of the vicinity close to the wafers converges to the set temperature.
However, with the conventional technique, the control parameter must be controlled on the basis of both the thermo-sensors A and B, and the adjustment operation is complicated. Further, in the above-described vertical type heat treatment equipment, the heater is divided into plural, for example, five, in the vertical direction so as to achieve the uniformity (face-to-face uniformity) of the vertical directional process temperature of the wafers mounted on the wafer board. Therefore, for each of the five heater segments, the above-described two types of the control parameters must be adjusted, thus making the adjusting operation very complicated and requiring a great deal of time.
An object of the present invention is to provide a temperature adjusting method and an apparatus therefor, which can be easily achieved and operated in the case where the difference in temperature between both of a temperature detection unit for adjustment and a temperature detection unit for processing is examined prior to carrying out a real process.